Circulation & Gas Circulation & Gas ExchangeExchange

Chapter 42, Campbell, 6th edition Nancy G. Morris

Volunteer State Community College

Exchange of materialsExchange of materialsbetween organism and environment:between organism and environment:

always occurs across a moist membrane

nutrients, gases, and wastes diffuse across membrane

molecules must be dissolved in water in order to diffuse across

Exchange of materials…Exchange of materials…

In protozoans, the entire surface is used for exchange.

Simple animals like sponges and cnidarians are constructed so that each cell is exposed to the surrounding water. (What pattern of construction permits this?)

What about triploblastic What about triploblastic animals?animals?

some cells are isolated from the surrounding environment

they require specialized organs for exchange with the environment

AND special systems for internal transport through body fluids to the cells

What are the advantages of specialized organs with an internal transport system?

1) reduces distance over which molecules must diffuse to enter & leave a cell AND

2) permits regulation of internal body fluids

Circulation in AnimalsCirculation in AnimalsTransport systems functionally connect

body cells with the organs of exchange.

Diffusion alone is too slow for complex multicellular animals.

The time of diffusion is proportional to the square of the distance the chemical must travel:

if a glucose molecule takes 1 second to diffuse 100µm, it will take 100 seconds to diffuse 1 mm.

The presence of a circulatory system The presence of a circulatory system reduces the distance a substance reduces the distance a substance must diffusemust diffuse……

because it connects the aqueous because it connects the aqueous environment of the cell with environment of the cell with organs specialized for exchange.organs specialized for exchange.

For example,

O2 diffuses from air across thin epithelium in the lung into the blood.

Oxygenated blood is carried via the circulatory system to all parts of the body.

As blood passes through capillaries in the tissues, O2 diffuses from the blood into the cells across the plasma membrane.

CO2 is produced by the cells and moves in the opposite direction.

The circulatory system…The circulatory system…

not only moves gases, but is a critical component in maintaining homeostasis of the body.

Blood passes from cells through organs (liver, kidneys) that regulate the nutrient and waste content of the blood.

Circulation in AnimalsCirculation in Animals

Invertebrates have either a gastrovascular cavity or a circulatory system for internal transport.

GASTROVASCULAR CAVITIESGASTROVASCULAR CAVITIES

In sponges & cnidarians, nutrients have only a short distance to diffuse to the outer cell layer. (Figure 42.1)

In flatworms & other platyhelminthes, no cell is more than a few mm away from the body surface.

Complex multicellular animals require some type of circulatory system.

OPEN CIRCULATORY SYSTEMSOPEN CIRCULATORY SYSTEMS

Hemolymph bathes the internal organs directly while moving through sinuses (Figure 42.2a)

Hemolymph acts as both blood and interstitial fluid

Relaxation of the heart draws hemolymph through the ostia into the vessel.

Insects, arthropods, mollusks

CLOSED CIRCULATORY SYSTEMSCLOSED CIRCULATORY SYSTEMS Blood is confined to vessels and Blood is confined to vessels and

interstitial fluid is presentinterstitial fluid is present

Heart (or hearts) pumps blood into large Heart (or hearts) pumps blood into large vesselsvessels

Major vessels branch into smaller ones Major vessels branch into smaller ones which supply blood to organs (Figure which supply blood to organs (Figure 42.2b)42.2b)

In the organs, materials are exchanged In the organs, materials are exchanged between the blood and the interstitial between the blood and the interstitial fluid bathing the cells.fluid bathing the cells.

Annelids and vertebratesAnnelids and vertebrates

CARDIOVASCULAR SYSTEMCARDIOVASCULAR SYSTEM

A A closedclosed circulatory circulatory systemsystem

consists ofconsists of1) a heart1) a heart

2) blood vessels2) blood vessels

3) blood3) blood

Closed cardiovascular systems Closed cardiovascular systems

A heart has one A heart has one atriumatrium or two or two atriaatria, chambers , chambers that receive blood, and one or two that receive blood, and one or two ventriclesventricles, , chambers that pump blood out.chambers that pump blood out.

ArteriesArteries carry blood away from the heart to carry blood away from the heart to organs where they branch into smaller organs where they branch into smaller arteriolesarterioles that give rise to microscopic that give rise to microscopic capillaries.capillaries.

Capillaries rejoin to form Capillaries rejoin to form venulesvenules, which converge , which converge to form to form veinsveins that return blood to the heart. that return blood to the heart.

CapillariesCapillaries Capillaries have thin, porous walls

and are arranged into networks called capillary beds that infiltrate each tissue.

The capillary wall is a single cell thick.

This is the site of chemical exchange between blood & interstitial fluid..

Fish: 2-chambered heartFish: 2-chambered heart

one atrium & one ventricle. (Fig 42.3a)

Blood pumped from the ventricle goes to the gills. O2 diffuses into the gill capillaries and CO2 diffuses out.

Gill capillaries converge into arteries that carry blood to capillary beds in other organs. Blood from the organs travels through veins to the atrium, then into the ventricle.

Fish: 2-chambered heartFish: 2-chambered heart Blood flows through two capillary beds

during each complete circuit: one in the gills and the second in the organ systems (systemic capillaries).

As blood flows through a capillary bed, blood pressure drops substantially (due to the resistance of the numerous small vessels).

Blood flow to the tissues and back to the heart is aided by swimming motions.

2-chambered heart2-chambered heart

1 atrium & 1 ventricle in fish

Amphibians: 3-chambered heartAmphibians: 3-chambered heart two atria and one ventricle (Fig. 42.3b)

Blood flows in a double circulation scheme through:1) 1) pulmocutaneous circuitpulmocutaneous circuit (to lungs and (to lungs and

skin)skin)

2) 2) systemic circuitsystemic circuit (to all other organs) (to all other organs)

Blood flow pattern: ventricle -> lungs & skin-> left atrium -> ventricle -> all other organs -> right atrium

3-chambered 3-chambered heartheart

• 2 atria & 1 ventricle of amphibian

Amphibians: 3-chambered Amphibians: 3-chambered heartheart

There is some mixing of oxygen-rich and oxygen-poor blood in the single ventricle.

A ridge present in the ventricle diverts most of the oxygenated blood to the systemic circuit and most of the deoxygenated blood to the pulmonary circuit.

Reptiles: 3-chambered heartReptiles: 3-chambered heart

most reptiles (except crocodilians) ventricle is partially divided

providing for double circulation: 1) a systemic circuit 2) a pulmonary circuit

partial division of ventricle reduces mixing of oxygenated and deoxygenated blood

Birds & mammals: 4 Birds & mammals: 4 chamberschambers

Double circulation: 1) systemic

2) pulmonary complete septum eliminates mixing of

oxygenated and deoxygenated blood separation greatly increases the

efficiency of O2 delivery to the cells

4-chambered 4-chambered heartheart

• 2 atria & 2 ventricles

• complete seperation of oxygenated and deoxygenated blood

• right heart drives pulmonary circulation

• left heart dives systemic circulation

• complete separation of oxygenation & deoxygenated blood

Human heart:Human heart:

located beneath the sternum

cone-shaped about size of fist

surrounded by pericardium (2 layers)

cardiac muscle tissue

atria collect blood returning to heart

ventricles are powerful pumps

Four valves of human Four valves of human heart.heart.

Valves are flaps of connective tissue. Atrioventricular valves –

found between atria & ventricles prevent backflow of blood

Semilunar valves- located where aorta leaves left

ventricle located where pulmonary arteries

leave the right ventricle

A heart murmurA heart murmur

is a defect in one or more of the valves that allows backflow of blood.

Heart’s rhythmic beat:Heart’s rhythmic beat:

Cardiac muscle is myogenic (self-excitable).

contracts without input from the nervous system

tempo is controlled by the sinoatrial node (SA) sometimes called the pacemaker.

SA nodeSA node

located in right atrium near the entrance of the superior vena cava

composed of specialized muscle tissue with characteristics of both muscle and nervous tissue

contraction of SA causes a wave of excitation to spread rapidly from the node causing the two atria to contract in unison

AV nodeAV node

second mass of specialized tissue

receives the wave of excitation from SA

impulse is delayed at the AV node for 0.1 second to ensure that the atria are completely empty before the ventricles contract

impulse is then carried by a mass of specialized fibers, Bundle of His, throughout the ventricle walls

Heart rateHeart rate controlled by SA

influenced by:1) two antagonistic sets of nerves–

one speeds contractions and the other slows contractions

2) hormones influence the SA node – epinephrine increases heart rate

3) other factors: body temperature & exercise influence heart rate